独立准直器调强放疗系统的验收测试

目的 建立IC_IMRT系统的验收测试方法并完成该系统的验收测试.方法 采用NE2571电离室和2570剂量仪测量加速器的启动特性和下咽、肺及宫颈癌3个病例的等中心和其他剂量特征点的绝对剂量.采用Mapcheck2二维半导体矩阵验证基本测试例和3个病例的二维平面剂量分布.基本测试例由矩形或方形射野组成,分别为2 cm×2 cm、5 cm×5 cm、10 cm×10 cm、20 cm×20 cm、2 cm×10 cm、10 cm×2 cm、5 cm×20 cm和20 cm×5 cm的对称射野,2 cm×2 cm(x1=4cm、y1=10 cm,χ2=-2 cm、y2=-8 cm)和5 cm×5 cm(x1=-2 cm、y1=-5 cm,χ2=7 cm、y2=10cm)的非对称射野及由5个20 cm ×4 cm的射野合成的20 cm×20 cm的条状叠加野.采用γ分析法比较测量和计算的剂量分布,通过率标准为3 mm/3%≥90%.结果 当加速器输出跳数达到4即可保证2%的剂量精确性;对所有测试例等中心及特征点的绝对剂量误差最大为-3.67%;在全部11个基本测试野和3个病例的24个照射野中只有条状叠加野和下咽癌病例2个野的通过率稍低于90%,分别是83.6%、88.3%和89.7%.3个计划的实施时间依次是15、14、27 min.结论 测试结果总体满足临床要求,系统可用于患者治疗.

Abstract：

Objective To perform an acceptance test for the IMRT system with independent collimator. Methods An ion chamber dosimeter were used to measure the startup characteristics of the accelerator and the absolute dose at isocenter and given characteristic points for three clinical cases ( a lower nasopharyngeal carcinoma, a lung cancer and a cervical cancer). The characteristic points represented the organs at risk or the target. A Mapeheck2 was used to measure dose maps of basic test fields and the treatment fields for the clinical cases. The basic test fields were as follows: 1 ). Symmetric fields in size of 2 cm ×2 cm, 5 cm ×5 cm, 10 cm× 10 cm, 20 cm ×20 cm, 2 cm × 10 cm, 10 cm ×2 cm, 5 cm ×20 cm and 20 cm ×5 cm;2). Asymmetric fields in size of 2 cm ×2 cm (x1 =4 cm, y1 = 10 cm;x2 = -2 cm, y2 = -8cm) and 5 cm ×5 cm (x1 = -2 cm, y1 = -5 cm;x2 =7 cm, y2 = 10 cm) ;3) A 20 cm ×20 cm composite field composed of five 20 cm× 4 cm narrow bar fields side by side. Gamma Index was used to compare calculated and corresponding measured dose distributions. When the criterion was 3% dose difference or 3 mm distance-to-agreement, the pass rate was required to be more than 90%. Results The accuracy of machine output was better than 2% when machine monitor units increased to 4. Among all basic test fields and all the treatment fields of three clinical cases, the maximal absolute dose error was -3.67%, and only the composite test field and two treatment fields of the lower nasopharyngeal carcinoma case had a pass rate slightly less than 90%, which were 83.6%, 88. 3% and 89. 7% ,respectively. For the three clinical cases the treatment delivery times were 15, 14, and 27 minutes, respectively. Conclusions The overall commissioning results are acceptable, and the system can be used in clinic.

Commissioning of intensity - modulated radiation therapy system with independent collimator

Objective To perform an acceptance test for the IMRT system with independent collimator. Methods An ion chamber dosimeter were used to measure the startup characteristics of the accelerator and the absolute dose at isocenter and given characteristic points for three clinical cases ( a lower nasopharyngeal carcinoma, a lung cancer and a cervical cancer). The characteristic points represented the organs at risk or the target. A Mapeheck2 was used to measure dose maps of basic test fields and the treatment fields for the clinical cases. The basic test fields were as follows: 1 ). Symmetric fields in size of 2 cm ×2 cm, 5 cm ×5 cm, 10 cm× 10 cm, 20 cm ×20 cm, 2 cm × 10 cm, 10 cm ×2 cm, 5 cm ×20 cm and 20 cm ×5 cm;2). Asymmetric fields in size of 2 cm ×2 cm (x1 =4 cm, y1 = 10 cm;x2 = -2 cm, y2 = -8cm) and 5 cm ×5 cm (x1 = -2 cm, y1 = -5 cm;x2 =7 cm, y2 = 10 cm) ;3) A 20 cm ×20 cm composite field composed of five 20 cm× 4 cm narrow bar fields side by side. Gamma Index was used to compare calculated and corresponding measured dose distributions. When the criterion was 3% dose difference or 3 mm distance-to-agreement, the pass rate was required to be more than 90%. Results The accuracy of machine output was better than 2% when machine monitor units increased to 4. Among all basic test fields and all the treatment fields of three clinical cases, the maximal absolute dose error was -3.67%, and only the composite test field and two treatment fields of the lower nasopharyngeal carcinoma case had a pass rate slightly less than 90%, which were 83.6%, 88. 3% and 89. 7% ,respectively. For the three clinical cases the treatment delivery times were 15, 14, and 27 minutes, respectively. Conclusions The overall commissioning results are acceptable, and the system can be used in clinic.